TPS miniCHEM-pH, Handbook, Page: 17 / 28

Page 17
Span Calibration
3. Place both sensors into a small sample of pH buffer, that is several pH away
from pH7 (e.g. pH4.00 or pH9.23). Ensure that the bulb and reference junction
are both covered (see diagram in step 6, above).
DO NOT place the electrodes
directly into the buffer bottle. Discard the used buffer after use.
NOTE: pH buffers above pH9 are highly unstable. Avoid using these
buffers if possible. Discard immediately after use.
pH4.00 buffer is recommended for its stability. Most users report
readings up to pH12 to be more accurate when using this buffer
than when using pH9.23 or pH10.00 buffer for span calibration.
4. When the reading has stabilised, adjust the
SPAN
control until the display
shows the value of the buffer. The pH4.00 buffer supplied by TPS lists the pH
value of the buffer at various temperatures.
5. Rinse the pH and ATC sensors in distilled water and blot them dry.
6. The mini CHEM -pH is now calibrated and ready for pH measurements.
4.2 Calibration Notes
1. An Asymmetry (Zero) calibration should be performed at least weekly. In
applications where the electrode junction can become blocked, such as dairy
products, mining slurries etc, an asymmetry calibration may have to be done
daily.
2. A full 2-point Asymmetry and Span calibration should be performed at least
monthly. Of course, more frequent calibration will result in greater confidence
in results.